Early structural and functional changes in the brains of individuals at risk for developing dementia of the Alzheimer type (DAT) are not well understood. Typically a diagnosis of DAT is made using neuropsychological performance testing and clinical evaluation. Previous work by our group and others has identified a preclinical phase of DAT that is associated with a constellation of changes in biomarkers including decreased cerebral spinal fluid (CSF) Abeta42 (AP42) levels, increased fibrillar amyloid deposits in the brain as detected by PET (using Pittsburgh B compound (PIB)), and increased atrophy, particularly within the hippocampus. An interaction exists between these biomarkers and risk factors for DAT such as family history and genotype (ie., apolipoprotein E (APOE). The exact sequence of preclinical events, and their effects on neuronal dysfunction that leads to DAT, remain unclear. Recent advancements in MR imaging could provide unique information in this regard. Specifically three techniques- resting state functional connectivity MRI (fcMRI), diffusion tensor imaging (DTI), and arterial spin labeling (ASL) perfusion imaging, could provide sensitive measures of neuronal function (fcMRI), cerebral blood flow (ASL) and white matter integrity (DTI). Repeated longitudinal measures using these neuroimaging techniques could add new information concerning the temporal course associated with the very earliest changes in brain function associated with DAT. This project has 3 aims: Aim 1: Changes in neuronal structure using fcMRI, ASL and DTI in a cross-sectional analysis will be correlated with age, APOE genotype, and biochemical and behavioral biomarkers. Aim 2. Subjects followed longitudinally with repeat fcMRI, ASL, and DTI will provide a temporal profile of the sequence of changes in neuroimaging biomarkers. Aim 3: Associate the rates of change over time in fcMRI, resting cerebral blood flow, and radial diffusivity in DTI measures with cognitive decline (Clinical Core), changes in cortical amyloid load as assessed by PIB (Project 1), changes in CSF biomarkers (Project 2), and neuropsychological measures (Project 3).